This invention relates to photodetector devices for detecting the presence of particulate matter in a gaseous medium such as air.
Such devices, generally speaking, have long been known and used in the prior art. See, for example, the smoke measuring transducer disclosed in U.S. Pat. No. 4,155,653 issued to A. San Miguel, et al. on May 22, 1979 and the particle detector disclosed in U.S. Pat. No. 4,245,910 issued to S. Kallander on Jan. 20, 1981. The first mentioned prior art device utilizes photoelectric detection by means of a single light beam passing between an emitter and a detector across a chamber containing air such tnat the amount of smoke or particulate matter in the air can be measured by determining the opacity or transmissivity thereof. The second prior art device also employs a single light emitter and detector wherein the emitter is disposed at one of two focal points in an elliptical reflecting chamber. The collector is placed at the other focal point so that light from the emitter is not only beamed directly against the collector but is also reflected off of the surrounding elliptically-shaped chamber surface against the collector. Numerous other arrangements of single beam photodetector systems for use in dust detection are also known in the prior art.
These prior art detectors thus sense the average opacity of a gas, such as air, contained in a detection chamber to provide a measure of the average amount of particulate matter contained in the gas. Such detectors are not adapted to sense the presence of individual dust particles in the gas which may be traveling at high speeds, as, for example, in a carburetor air intake system. Neither are such devices adapted to react extremely quickly to such individual particles so as to rapidly alert an engine operator to the presence of a small quantity of potentially engine damaging particles. These devices are adapted to measure the presence of particulate matter in a gas by sensing the attenuation of a light beam directed across a gas filled chamber rather than by sensing the interruption of the beam caused by particles flowing through the chamber at high speeds.
By means of my invention, these and other difficulties encountered in the prior art are substantially reduced or eliminated.